Thieves rob De Beers and Omega stores in shopping centre on Saturday.
A former Scotland Yard commander told BBC 4 radio that the raid on the De Beers and Omega stores in the City of London this weekend could have been an inside job.
Raiders stole an unknown quantity of luxury jewellery and watches from the stores in the Royal Exchange shopping centre, after smashing through the display windows with sledgehammers at around 10pm on Saturday night.
The thieves, who broke into the complex, which is closed on the weekends, are believed by police to have driven up and left in a red BMW car.
Former Flying Squad officer John O’Connor has claimed that the raiders may have had inside assistance.
He said on the BBC Radio 4 Today programme: "The villains did not drive up on the off-chance they could get through security gates.
"There is always the suspicion that they had somebody on the inside."
Police are currently looking through CCTV footage in an attempt to identify the robbers.
City of London Police Major Investigations Team senior investigating officer, detective chief inspector Steven Chandler, said: “We are currently following a number of lines of enquiry and I can reassure the public that every effort is and will be directed to bringing those responsible to justice. We need the assistance of the public in tracing the car used in the offence, the criminals involved and the items stolen".